The present invention relates to speech scrambling techniques and systems and in particular to a frequency or time domain speech scrambling technique and system which does not require any frame synchronization.
Communication security has become one of the major attractive problems in signal transmission and is getting more and more massive and complicated due to the rapid progress in communication developments.
At present the newest technique of secure speech communications is the use of a scrambled digital signal by the sender to transmit digits to receiver who in turn descrambles digital signal in conformity with sender's scrambling and transform them into an analog signal. However, this means of communication includes the following disadvantages:
1. Apparently, the sender and receiver require very accurate synchronization. This process not only makes implemention difficult and cost higher, but also is subject to transmission interruptions under poor channel conditions.
2. The current cost of setting up digital transmission facility is high.
The purpose of this invention is to provide improvements in transmission techniques subject to the above technical disadvantages, so that the synchronization problems can be solved (synchronization is not required) and a speech scrambling method offering a high degree of security is introduced. However, the means of signal communications adopted in this invention is still the conventional linear mode of transmission, i.e., analog transmission.